1. Field of the Invention
This invention relates to aircraft retractable landing lights. Specifically, the invention is directed to an aircraft retractable landing light having electronic position control and switching with manual lighthead retraction capability.
2. Description of the Related Art
Landing lights are mounted to aircraft to illuminate the area forward of the aircraft during night operations on taxiways and runways. A “retractable landing light” is a remotely controlled, articulating light that can be stowed flush with the outside surface of the aircraft when not in use, reducing aerodynamic drag on the aircraft. The retractable landing light's lamp is housed in a lighthead. The lighthead is in turn hingedly affixed to a housing assembly, which is mounted to the airframe. The lighthead is extended for use and retracted to a stowed position by means of an unsealed torque-amplifying transmission mechanism driven by an electric motor. The lighthead is held in place by an electromechanical brake. When the flight crew actuates a remote control to an “Extend” position, the brake is released by applying electrical power to the brake's coil. Electrical power is simultaneously applied to the motor, causing the motor's output shaft to turn, driving the transmission. The lighthead then extends to a predetermined position, aiming the lamp to illuminate the area forward of the aircraft. Power is then removed from the motor and the brake, causing the lighthead to stop moving. The brake re-engages, preventing the motor's output shaft from turning. The holding force of the brake is amplified by the transmission mechanism, effectively holding the lighthead in position against the force of the windstream encountered by an aircraft in flight. The motor and brake are also simultaneously activated when the remote control is placed in a “Stow” position. However, power is applied to the motor so as to cause the motor's output shaft to rotate counter to the direction used to extend the lighthead. When the lighthead is flush with the surface of the aircraft, power is again removed simultaneously from the motor and brake, holding the lighthead in the stowed position. The lamp may be automatically switched on by means of a limit switch after the lighthead is extended and then switched off when the lighthead is retracted. Alternatively, the lamp may be manually controlled by a switch in the cockpit.
Prior retractable landing lights suffer from a number of shortcomings. In particular, prior retractable landing lights utilize electromechanical limit switches to detect the lighthead's position, and electromechanical relays for control of the motor, brake, and lamp. Electromechanical switches and relays have limited operational life due to mechanical wear. In addition, these switches and relays generate electromagnetic interference due to arcing at their electrical contacts. Electromechanical switches also hinder the ability to change the operational characteristics of the retractable landing light. It is desirable to change such operational characteristics as the extension angle of the lighthead and the switching sequence of the lamp, brake, and motor in order to meet the particular needs of various models of aircraft.
Another drawback of electromechanical switches is that they do not lend themselves to precise position control due to the limited resolution of actuators. Precise position control is desirable to aim the lamp at the proper angle. If the lighthead is extended to a smaller angle than desired, the lamp will be aimed too close to the aircraft. Conversely, if the lighthead extension angle is too great, the lamp will be aimed too far ahead of the aircraft. Both conditions result in a reduction in visibility for the flight crew. Attempts to implement more precise mechanical position controls in prior retractable landing lights have resulted in more complex actuators, reducing the reliability of the retractable landing light. Mechanical wearing of the actuators, combined with changes in setting due to vibration, also contributes to shifting of the lamp extension angle over time, requiring regular maintenance to re-adjust the lighthead to the proper angle.
A further disadvantage of electromechanical switches and relays is that current flow through the motor, brake and lamp is limited only by the capacity of the aircraft's electrical system and wiring. This places significant stress on the relay contacts, motor, brake, and lamp, causing these components to suffer reduced service life. “Soft” starting of the motor, brake, and lamp is desirable to limit electromagnetic emissions and maximize the life of these components.
A retractable landing light may be installed into more than one model of aircraft. However, design differences between models of aircraft usually necessitate a change in the extension angle setting of the lighthead so that the lamp is properly aimed for a particular aircraft. This involves a time-consuming manual adjustment of position-control limit switches and repeated cycling of the retractable landing light. Means for pre-setting selectable extension angles for different models of aircraft is desired in order to reduce the amount of maintenance work required to install the retractable landing light into two or more models of aircraft.
Prior retractable landing lights utilize an open gearbox. Over time, exposure to the elements when the lighthead is extended causes a loss of gearbox lubrication. Low viscosity grease is used to counter this loss, but at the expense of gearbox efficiency, particularly at low temperature extremes.
Retractable landing lights inherently have a failure mode whereby the lighthead cannot be retracted. The aircraft cannot be dispatched in this condition, requiring maintenance personnel to remove and replace the retractable landing light. This can cause significant delays in the dispatch of the aircraft, particularly if the failure occurs at a remote location with limited maintenance capability. Although prior retractable landing lights have included manual retraction capability, the release mechanisms are slow and cumbersome.
Some improvements in remotely articulating aircraft lights have been made, such as Hamilton et al. U.S. Pat. No. 6,315,435 B1. However, Hamilton et al. teaches the use of potentiometers having wiping elements in contact with a resistive element. Potentiometers are subject to wear-out, limiting the service life of the aircraft light. Further, Hamilton does not teach how to preconfigure the operating envelope of an articulating light for different aircraft models, since the preset positions disclosed in Hamilton define only the operating envelope limits for the lighthead. Changes in the operating envelope to accommodate different aircraft models must be made by trial-and-error upon installation of the light into the aircraft. Also, Hamilton does not disclose how to reduce electromagnetic emissions and extend the service life of the motor brake and motor. In Metz et al., U.S. Pat. No. 5,355,131, an aircraft landing light utilizing contactless position sensing is taught. However, the position sensing disclosed in Metz does not accommodate reconfiguration of the operating envelope for different aircraft models, necessitating trial-and-error adjustment.
There is a need to limit inrush currents and eliminate the low-reliability relays and switches associated with retractable landing lights. There is also a need to provide a more reliable, precise, and easily reconfigurable means of controlling the position of the retractable landing light's lighthead. There is a further need to protect the gearbox from the elements. Finally, there is a need to provide capability for aircraft with failed retractable landing lights to delay repair and to dispatch with the failed light in place.